Broadband wireless communication resource assigning method, base station apparatus and terminal apparatus

ABSTRACT

A method of wireless communication for communication between a base station and a plurality of terminal apparatuses, the method including: dividing an available frequency into a plurality of segments and notifying control information to the terminal apparatus, the control information including setting of a segment of the plurality of segments, communication quality of which will be fed back by the terminal apparatus, and cancellation of a segment of the plurality of segments, communication quality of which has already been fed back from the terminal apparatus; and feeding back communication quality related to a predetermined segment to the base station in accordance with the control information by the terminal apparatus.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. application Ser. No. 12/279,750, filedAug. 18, 2008 now U.S. Pat. No. 8,290,001. This application relates toand claims priority from Japanese Patent Application No. 2006-091137,filed on Mar. 29, 2006. The entirety of the contents and subject matterof all of the above is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a transmitting and receiving apparatusused in a broadband wireless communication system and a transmitting andreceiving method.

BACKGROUND ART

In recent years, in broadband wireless communication systems, OFDMA thatassigns different terminal apparatuses to respective parts of the systemband has been attracting attention. OFDMA is a multi dimensional accesstechnology based on OFDM in which subcarriers perpendicular to eachother are arranged on a frequency axis, and a segment in which aplurality of subcarriers are bundled up is set as a resource unit, and abase station apparatus assigns different segments to respective terminalapparatuses.

To increase the frequency usage efficiency of the wireless communicationsystem using OFDMA, it is effective to compare the communication qualityof every segment in each terminal apparatus so as to assign each segmentto the terminal apparatus having a preferable quality. In the wirelesscommunication system, communication quality changes with time.Accordingly, in the case of downlink communications, each terminalapparatus measures the communication quality at a specified spacing, andfeeds it back to the base station apparatus. The technology todynamically assign the frequency segment whose communication quality ispreferable to each terminal apparatus is called a frequency schedulingtechnology, and it has been studied flourishingly (for example, refer toPatent Document 1 or Non-Patent Document 1).

As the representative algorithms of the scheduling, there are knownthree kinds that are: (1) Maximum CIR Algorithm; (2) Round RobinAlgorithm; and (3) Proportional Fairness Algorithm. In the algorithm(1), transmission opportunities are assigned with priority to a terminalapparatus whose communication quality is preferable. As thecommunication opportunities with the terminal apparatuses near the basestation apparatus increase, communication opportunities with theterminal apparatuses at distant places decrease; therefore, it is ascheduling algorithm in which the service differences become large amongthe terminal apparatuses. In the algorithm (2), the communicationopportunities are assigned to all terminal apparatuses equally. Incomparison with (1), as the communication opportunities with theterminal apparatuses at the distant place are increased, the throughputof the base station apparatus is declined. In the algorithm (3), a valueof (real-time communication quality)/(average communication quality) isused as the evaluation value, and the transmission opportunities areassigned with priority to the terminal apparatus whose evaluation valueis large, and accordingly, it is an algorithm in which the communicationopportunities are equal, and the frequency usage efficiency is superiorto (2). However, it is a problem that the base station apparatus mustprecisely know the real-time downlink communication quality in everywireless terminal apparatus.

-   Patent Document 1: Japanese Patent Application Laid-Open Publication    No. 2002-252619-   Patent Document 2: Japanese Patent Application Laid-Open Publication    No. 2005-244958-   Non-Patent Document 1: “MC-CDM System for Packet Communications    Using Frequency Scheduling”, IEICE Technical Report, RCS2002-129,    July, 2002, p. 61-66-   Non-Patent Document 2: 3GPP2 C.S0024-A “cdma2000 High Rate Packet    Data Air Interface Specification” (page 11-80, 2004 Mar. 31)-   Non-Patent Document 3: 3GPP TR 25.814 V1.1.1, “3rd Generation    Partnership Project; Technical Specification Group Radio Access    Network; Physical Layer Aspects for Evolved UTRA (Release7)” (pages    18 and 24, 2006 February)-   Non-Patent Document 4: Jim Tomcik, “QFDD and QTDD: Technology    Overview”, Contributions on IEEE 802.20 Mobile Broadband Wireless    Access, IEEE C802.20-05/68r1, January 2006. (pages 79 to 84)

DISCLOSURE OF THE INVENTION

The Proportional Fairness in which both the throughput of the basestation apparatus and the communication opportunity equality (fairness)among the terminal apparatuses are attained has been already put topractical use in the cdma2000EV-DO (Evolution Data Only) system. In thesystem, the terminal apparatus uses 2,400 [bit/s] for an uplink band tofeed back communication quality information DRC value (Data RateControl, from Non-Patent Document 2) of 4 [bits] per one slot 1.67 [ms].2,400 [bit/s] is a number per one terminal apparatus when upon sharingone frequency segment by a plurality of terminal apparatuses. Forexample, in the case where 50 terminal apparatuses are connected with abase station apparatus, an uplink band of 2,400×50, i.e., 120,000[bit/s] is necessary at the base station apparatus.

The uplink band that is necessary for the feedback of the communicationquality information is in inverse proportion with the cycle in which theterminal apparatus feeds back DRC, and is in proportion with the numberof the frequency segments to be fed back. Therefore, when the abovefeedback is carried out at the 0.5 [ms] subframe spacing that is definedin the LTE (Long Term Evolution, cf. Non-Patent Document 3) of 3GPP,400,000 [bit/s] is needed as a result of 120,000 [bit/s]×1.67/0.5.Similarly, when a PRB (Physical Resource Block) of 375 [KHz] in which 25subcarriers of 15 [kHz] spacing that is defined to LTE are bundled up isconsidered as a frequency segment and also all feedbacks are carried outassuming the system band thereof as 100 [MHz], the base station's uplinkthroughput of about 107 [Mbit/s] is necessary as a result of400,000×100,000,000/375,000.

As mentioned above, a first problem to be solved by the presentinvention is to reduce the enormous uplink throughput of the basestation that the feedback information needs so as to improve the uplinkthroughput of useful user data.

With regard to the first problem, one solution is shown in PatentDocument 2. The method shown in Patent Document 2 is a method in whichthe terminal apparatus measures the communication quality of allfrequency segments, and feeds back only the information of the segmentswhose communication quality is preferable to the base station apparatus.Although it is true to be possible to reduce the feedback information bythis method, a problem is surely left at the point where the frequencysegments that the terminal apparatus chooses does not always guarantee ahigh downlink throughput to the terminal apparatus. Since the throughputis decided by (the number of communication bits per onecommunication)×(the number of communication times), to achieve a highthroughput, it is necessary to guarantee not only the communicationquality but also the number of communication times.

As mentioned above, a second problem to be solved by the presentinvention is to carry out a frequency segment assignment to guaranteemany numbers of communication times and preferable communication qualityto every terminal apparatus so as to increase the downlink throughput.To solve this second problem together, a solution of the first problemdifferent from that in the Patent Document 2 will be disclosed.

Meanwhile, it is assumed that the statistics values of communicationcapacity are different every frequency segment in the present invention,and the reason thereof will be explained.

In the present invention, it is assumed that spatial multiplexcommunications by beam-forming are carried out every frequency segmentin a broadband communication system. As mentioned in the first problem,in the broadband communication system, when the usage of all the segmentis permitted to all the terminal apparatuses, the feedback informationamount becomes enormous; therefore, for example, like the presentinvention, limiting segments available to each terminal apparatus isconsidered. As a result, since the combinations of the terminalapparatuses belonging to each segment are different, those spatialmultiplex interferences affecting to the circumference are notguaranteed to become uniform among the segments. This is the ground tothink that the statistics values of communication capacity are differentin each segment.

The phenomenon mentioned above may be considered as a state where FFR(Fractional Frequency Reuse, Non-Patent Document 4) is carried out in awide sense because the frequency segments to be used are different ineach direction viewed from the base station. Conversely speaking, whenthe FFR is carried out by some kind of method, the statistics values ofthe communication capacity do not become same in all the frequencysegments.

To solve the problems, the base station apparatus assigns segments whosenumber of communication times is large and whose communication qualityis high to each terminal apparatus so as to reduce the number of thefrequency segments that feed back DRC per a terminal apparatus.

In order to guarantee the number of communication times per a terminalapparatus, it is required that there are a small number of competitorsat the moment of the assignment of frequency segments.

When the base station apparatus transmits downlink packets by an Omnibeam pattern per frequency segment, there are competitors of the numberof the terminal apparatuses to which the frequency segment is assigned.In FIG. 1, an example in which the numbers of competitors are differentin respective frequency segment is shown. In the upper section of thefigure shows a frequency segment 1 and the lower section shows afrequency segment 2. The base station apparatus 12-1 and 12-2 outputOmni beam patterns 11-1 and 11-2 in different frequency segments,respectively. In the frequency segment 1, one terminal apparatus amongfive terminal apparatuses 13-1-a, b, c, d, e may communicate in eachslot, meanwhile in the frequency segment 2, either of two terminalapparatuses 13-2-a, b may communicate. Since the number of the terminalapparatuses that can communicate per one slot is one unit in eachsegment, there are 5 competitors in the segment 1, and there are 2competitors in the segment 2. In addition, while two base stationapparatuses 12-1 and 12-2 are shown in FIG. 1 to clearly show thecharacteristics of each frequency segment, in fact, these are the sameapparatus.

Further, in the case where the spatial multiplex communications arecarried out by directional beams in each frequency segment, there is thecase where terminal apparatuses whose directions are as away from thebase station as the spatial multiplex is possible do not becomecompetitors to each other in the schedule control. An example thereof isshown in FIG. 2. In the example of the frequency segment 1 shown in theupper section, the directions of the two terminal apparatuses 13-1-a, bviewed from the base station apparatus 12-1 are same; therefore, thespace division multiplex communications of both the terminal apparatusesby the directional beam 14-1-a is difficult. Therefore, the respectiveterminal apparatuses become competitors to each other. In contrast, inthe frequency segment 2, since the directions of the two terminalapparatus 13-2-a, b are different with each other, the spatialsegmentation multiplex communication by the directional beams 14-2-a, bis possible. Therefore, the respective terminals do not becomecompetitors to each other.

In consideration of the foregoing, an expected value of the number ofcommunication times per a frequency segment of each terminal apparatusis calculated by a reciprocal number of the number of the competitors.When the base station apparatus assigns the frequency segments to theterminal apparatus, the throughput improvement of the terminal apparatusis expected by assigning to the frequency segment whose expected valueis large. To calculate the number of the competitors, the spatialproperty of each terminal apparatus (the direction of each terminalapparatus) viewed from the base station apparatus, and assignmentinformation about on which terminal apparatus is assigned to whichfrequency segment are necessary.

Therefore, as means to guarantee the number of communication times pereach terminal apparatus, means to measure the spatial property of eachterminal apparatus and means to assign the terminal apparatus to eachfrequency segment are provided to the base station apparatus.

To increase the communication quality in each terminal apparatus, it isdesirable to assign the frequency segment whose communication quality ispreferable to each terminal apparatus. However, it is thought that, whenthe terminal apparatus disorderly feeds back DRC about the frequencysegment of each best N (N being an integer) as shown in the PatentDocument 2, a difference occurs among the number of the terminalapparatuses feeding back the DRC by the frequency segments as shown inFIG. 1, and it is assumed that the number of communication times cannotbe obtained in some terminal apparatuses.

Accordingly, the base station apparatus assigns the terminal apparatusto the frequency segment orderly so that the expected value of thenumber of communication times of each frequency segment increases ineach terminal apparatus. With that, to increase the downlink throughputof each terminal, it is desirable to measure the average and dispersionof the communication capacity of each frequency segment at each terminaland to assign each terminal apparatus to the frequency segment whosestatistics values (average and dispersion) of the communication capacityis high. While it is clear that the terminal apparatus throughputincreases by assigning the frequency segment whose average of thecommunication capacity is high, a reason why the terminal throughput isimproved when the dispersion is high will be described with reference toFIG. 3.

The upper section of FIG. 3 shows a graph in which the horizontal axisshows time and the vertical axis shows downlink communication capacity,and shows changes with time of the communication capacity about twoterminal apparatuses in a certain frequency segment. Averages anddispersions of communication capacities of both the terminal apparatusesare same, and the case where communication capacities thereofalternately exceed the average value is shown. Since the base stationapparatus chooses a better one (shown by bold line) of both the terminalapparatuses one after another, it is possible to increase the totalthroughput for the two terminal apparatuses by user diversity. The lowersection of FIG. 3 is same as the upper section except that thedispersion of the communication capacity is large. As is apparent fromthe figure, the larger the dispersion is, the higher the effect of userdiversity becomes, and it is possible to further increase the totalthroughput for the two terminal apparatuses. In addition, even if theaverage communication capacities of the two terminal apparatuses aredifferent, because the terminal apparatus whose instantaneous plus(positive) deviation of the average communication capacity of eachterminal apparatus is large is chosen one after another in theProportional Fairness, the effect of user diversity does not change.However, in the case where one of two frequency segments whosedispersions of the communication capacities are same but whose averagesare different is assigned to a certain terminal apparatus, it isdesirable to assign the frequency segment whose average is higher.

A concrete method of the above assignment will be described withreference to FIG. 4.

FIG. 4 shows a graph in which the horizontal axis shows downlinkcommunication capacity, and the vertical axis shows probability density,and shows a distribution of the communication capacity per eachfrequency segment about a certain terminal apparatus. An average of anaverage per each segment is defined as Ensemble Average. Thecommunication capacity to become the control target is defined asThreshold, and the occurrence probability of the communication capacityexceeding the Threshold is calculated per each frequency segment. TheThreshold is defined per each terminal apparatus. One of the occurrenceprobability calculation methods is shown. Upon assuming that thedispersion of the communication capacity of each frequency segment is anormal distribution, from the average value and the standard deviationvalue of the communication capacity, it is calculated per each segmentthat how many times a value obtained by subtracting the average valuefrom the above Threshold should be multiplied to be equivalent to thenormal deviation value. This calculated value corresponds to theoccurrence probability one-on-one.

To realize this calculation, means to measure the statistics values ofthe communication capacities about all the frequency segments in eachterminal apparatus, means to feed back the measurement result to thebase station apparatus by a cycle that is sufficiently longer than theDRC feedback, means to carry out the calculation of the occurrenceprobability of the communication capacity exceeding the Threshold basedon the communication capacity statistics values per each frequencysegment of all the terminal apparatuses in the base station apparatus,and means to assign the terminal apparatus per each frequency segmentare necessary.

To fuse the means to guarantee the number of communication times and themeans to guarantee the communication quality, it is a feature of themeans to assign the terminal apparatus to each frequency segment whichthe base station apparatus has that the means assigns the frequencysegment that has few competitors sharing the same segment and whoseaverage and dispersion of the communication capacity are high to eachterminal apparatus.

According to the assignment shown above, the base station apparatuslimits the segment that feeds back the communication quality information(corresponds to DRC) to the terminal apparatus to M segments (M<N: Nbeing the number of all the segments) and reduces the uplink bandnecessary for the feedback of the communication quality information. Theterminal apparatus feeds back the communication quality informationabout the assigned M segments to the base station apparatus per eachslot, and the base station apparatus carries out scheduling per eachslot based on the communication quality information of each terminalapparatus, and assigns a segment for transmitting the downlink datapackets to each terminal apparatus in a range of 0 to M segments pereach slot.

In a wireless communication system carrying out broadband packetcommunications, by assigning an available frequency segment per eachterminal apparatus, it is possible to reduce the feedback informationnecessary for downlink adaptation and to increase throughput of usefuluser data in the uplink communications. Further, by carrying out theassignment of the above-mentioned segment so as to guarantee manynumbers of communication times and high communication quality to eachterminal apparatus, it is also possible to increase the downlinkthroughput.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 is an explanatory diagram (1) about an expected value of thenumber of communication times per each frequency segment;

FIG. 2 is an explanatory diagram (2) about an expected value of thenumber of communication times per each frequency segment;

FIG. 3 is a diagram showing increase of a user diversity effect byincrease of the communication capacity dispersion;

FIG. 4 is a diagram showing communication quality distributions ofrespective frequency segments;

FIG. 5 is a diagram showing a best embodiment of a control methodaccording to the present invention;

FIG. 6 is a diagram showing an extract of a long-period control part ofthe control method according to the present invention;

FIG. 7 is a diagram showing an extract of a short-period control part ofthe control method according to the present invention;

FIG. 8 is a diagram showing an example of a message format to feed backstatistics values of a communication capacity;

FIG. 9 is a diagram showing an example of a message format to feed backinstantaneous values of a communication capacity;

FIG. 10 is an explanatory diagram about changes of expected values ofthe number of communication times upon a terminal apparatus additionassignment;

FIG. 11 is a diagram showing an example of a counting result ofoccurrence probability of high communication capacity;

FIG. 12 is a diagram showing an example of evaluation values to assign afrequency segment to a terminal apparatus;

FIG. 13 is a diagram showing an example of a message format to notify anassignment result of the frequency segment;

FIG. 14 is a diagram showing a best embodiment of a terminal apparatusaccording to the present invention;

FIG. 15 is a diagram showing a structure of a statistics valuecalculation part of the communication capacity;

FIG. 16 is a configuration diagram showing a structure of an indicatorgeneration part about the communication capacity instantaneous value;

FIG. 17 is a diagram showing a best embodiment of a base stationapparatus according to the present invention;

FIG. 18 is a diagram showing an example of relations of the number ofbits, an encoding rate, and a modulation method to the indicator;

FIG. 19 is a diagram showing an example (1) of control of frequencysegment assignment information in the base station apparatus;

FIG. 20 is a diagram showing an example (2) of control of frequencysegment assignment information in the base station apparatus; and

FIG. 21A-21B are a diagrams showing examples of a counting result of anexpected value of the number of communication times.

BEST MODE FOR CARRYING OUT THE INVENTION

In FIG. 5, a control method to carry out the present invention is shown.

A base station apparatus transmits a pilot signal per each slot (S1).While the terminal apparatus first carries out a cell search by use ofthe pilot and establishes a connection with the base station apparatus,herein, descriptions will be made on the supposition that the connectionis already established.

The terminal apparatus, on receiving the pilot signal, measures aninstantaneous value of a communication quality (SINR: Signal toInterference plus Noise Ratio) per each frequency segment and convertsthe same into a communication capacity by the expression of theShannon's channel capacity (S2), and continues adding the instantaneousvalue of the communication capacity and the square value thereof pereach segment over a plurality of slots and averages them at a specifiedcycle (period) and calculates statistics values (average and dispersionof the communication capacity) per each segment (S3), and clears thebuffer for the above addition. Further, the instantaneous value of thecommunication capacity is converted into an indicator at the next step(S4). The conversion into indicator is realized by a table look-up ofthe communication capacity. The value of the communication capacity maybe just fed back as it is, but it is desirable to convert the same intothe indicator so as to reduce the feedback information amount to feedback. In addition, it is only M segments (M<N) assigned by the basestation apparatus, among all the N segments, that are converted into theindicator of the communication capacity.

After the completion of the above process, the terminal apparatus sendscontrol information to the base station apparatus. The controlinformation shall include the following two kinds. That are: (1)statistics values of the communication capacity of each of all thefrequency segments (S5), and (2) the indicator showing the instantaneouscommunication capacity of the frequency segment assigned to the terminal(S6), that is all. With regard to (1), the terminal apparatus feeds backthe statistics values about all the N segments (average value andstandard deviation value) at a long cycle. With regard to (2), theterminal apparatus feeds back the indicator of the communicationcapacity instantaneous value of the M segments (M<N) assigned by thebase station apparatus, among all the N segments, at a short cycle pereach slot.

FIG. 8 shows an example of a format of the control signal feeds back theaverage value and the standard deviation of the communication capacity(S5 of FIG. 5). The first Message ID is an 8-bit value promised with thebase station apparatus, and it is for the purpose of showing that thefollowing information is the average value and the standard deviation ofthe communication capacity per each frequency segment. The second stageshows a terminal apparatus ID of the source of transmission.AveCapacitySegment #n and StdCapacitySegment #n (n being 0 to N−1, Nbeing the number of all segments) after the third stage show an averagevalue and a standard deviation of the communication capacity of afrequency segment n.

FIG. 9 shows an example of a format of the control signal to feed backthe indicator showing the instantaneous communication capacity of thefrequency segment assigned to the terminal (S6 of FIG. 5). The firstMessage ID is an 8-bit value promised with the base station apparatus,and it is for the purpose of showing that the following information isthe indicator which shows the instantaneous communication capacity. Thesecond stage shows the terminal apparatus ID of the source oftransmission. CapacityIndicator #m (m: 0 to M−1, M being the number ofthe frequency segments assigned to the terminal apparatus) after thethird stage is the indicator showing the instantaneous communicationcapacity of each frequency segment. The base station apparatus carriesout scheduling per each slot based on the indicator (S7 of FIG. 5), andassigns segments to transmit the downlink data packets to each terminalapparatus, 0 to M segments per each slot, among the segments that feedback the indicator. The base station apparatus that assigns the M piecesof the segments to the terminal apparatus in S9 of FIG. 5 grasps how Mpieces of the indicators are mapped to N pieces of the segments. If thesequence of the frequency segments (ascending sequence of the frequencysegments) that the base station apparatus notifies when the same assignsthe frequency segments to the terminal apparatus (S10 of FIG. 5), andthe sequence in the message of FIG. 9 are aligned, the mapping at thebase station apparatus side is possible. Even if this premise is broken,if the frequency segment ID is added to each indicator, the mapping atthe base station apparatus is possible; however, the feedbackinformation amount increases, therefore it is desirable to the premiseabove.

Here, the description is back to FIG. 5.

When the base station apparatus receives the feedback of the controlinformation (S6) from the terminal apparatus, the base station apparatusfirst carries out a choice of the terminal apparatuses to which downlinkpackets are sent based on the Proportion Fairness, among the terminalapparatus to which the frequency segments have been already assigned.The base station apparatus carries out the adaptation modulation basedon the indicator of the real-time communication quality fed back fromthe terminal apparatus, and generates downlink packets corresponding torespective addresses per each frequency segment (S7).

Next, an expected value of the number of communication times inrespective all the frequency segments per each terminal apparatus iscalculated (S8). Herein, the arrival direction estimation result (in thecase to carry out the spatial multiplex communication per each frequencysegment) by the pilot signal included in the uplink signal, and thefrequency segment assignment information at the present are referred to.Hereinafter, a calculation method of the expected value will bedescribed.

When one terminal apparatus is assigned newly to the frequency segment 1of FIG. 1, since the frequency segments that have been shared by fiveunits are shared by six units, the expected value of the number ofcommunication times becomes ⅙. In the same manner, an expected valueabout the frequency segment 2 becomes ⅓.

When one terminal apparatus is assigned newly to the frequency segment 1of FIG. 2, if the angle difference with the already assigned terminalapparatus is the Threshold or below (for example, 15 degrees), thefrequency segments and the directional beams are shared by threeterminal apparatuses, thereby, the expected value of the number ofcommunication times becomes ⅓; however, when the angle difference ismuch more than the threshold value, since the terminal apparatus to beassigned newly can perform the spatial multiplex communication with twoterminal apparatuses, the expected value becomes 1. The abovedescription is shown in FIG. 10.

The upper section of FIG. 10 shows the case in which a frequency segmentis assigned to a terminal apparatus 13-1-c that is in the same directionas that of two terminal apparatuses 13-1-a, b. In this case, because ofthe difficulty of the space division multiplex communication, theexpected value of the number of communication times about each terminalapparatus becomes ⅓. The lower section of FIG. 10 shows the case where afrequency segment is assigned to a terminal apparatus 13-1-c that is ina direction different from that of the two terminal apparatuses 13-1-a,b. In this case, since the space division multiplex communication ispossible with the existing terminal apparatuses, the expected valuebecomes 1 about the new terminal apparatus.

When the calculation method of the expected value is generalized, it canbe expressed by the inverse number of the number of the terminalexisting within X degree from the terminal apparatus. About the Xdegree, 360 degrees are equivalent to the X degree about the Omni beam,and the smallest interval between the main beam direction and the nulldirection at which the array antenna of the base station apparatus canbe generated is equivalent to X degree about the directional beam.

With the explanations in the foregoing, the calculation method of theexpected value ends.

When the expected value calculation of the number of communication timesof each terminal apparatus is completed, together with the statisticvalues of the communication capacity of each frequency segment of eachterminal apparatus obtained from the feedback control information (S5)about all the frequency segments from the terminal apparatus, thefrequency segments to be assigned to each terminal apparatus is decided(S9).

First, as shown in FIG. 11, from the average and the standard deviationof the communication capacity that the terminal apparatus feeds back,the communication capacity to become the control target is defined as aThreshold, and the occurrence probability of the communication capacityexceeding the Threshold (high communication capacity) is calculated pereach frequency segment. The concrete calculation procedure is shownbelow.

When a probability density function of the communication capacity “c”about the frequency segment “s” of the terminal apparatus “u” is definedas fu,s(c), the probability Fu,s(cT) exceeding the Threshold (CT) isdefined according to the following expression.

$\begin{matrix}{{F_{u,s}\left( c_{T} \right)} = {\int_{c}^{\infty}{{f_{u,s}(c)}{\mathbb{d}c}}}} & {{Expression}\mspace{14mu} 1}\end{matrix}$

It is supposed that this probability density function fu,s(c) followsthe normal distribution of the average μu,s and the standard deviationσu,s.

$\begin{matrix}{z = \frac{c - \mu_{u,s}}{\sigma_{u,s}}} & {{Expression}\mspace{14mu} 2}\end{matrix}$

When the above variable conversion is carried out, under the aboveassumption, the probability Fu,s(cT) is expressed according to thefollowing expression.

$\begin{matrix}{{F_{u,s}\left( c_{T} \right)} = {\int_{{({{cT} - \mu_{u,s}})}/\sigma_{u,s}}^{\infty}{{f_{u,s}(z)}{\mathbb{d}z}}}} & {{Expression}\mspace{14mu} 3}\end{matrix}$

Therein, f(z) is a probability density function according to thestandard normal distribution. The initial point of the integral calculusof this expression shows that how many times the standard deviation σu,sshould be multiplied to correspond to CT to the average μu,s of eachfrequency segment. The above integral calculus is made at each time orcarried out by a table look-up of the calculation value with respect tothe initial point of the integral calculus.

When the table of FIG. 11 is filled, it is possible to calculate theevaluation function for the assignment per each frequency segment asshown in FIG. 12. The inputs are: the expected value of the number ofcommunication times; and the high communication capacity incidencecalculated in relation with FIG. 11. In the example of FIG. 12, aproduct of the expected value of the number of communication times andthe high communication capacity incidence is calculated, and theevaluation function value (assignment evaluation value) is calculated.The evaluation function is not limited to the form of the product of theboth variables. The base station apparatus assigns higher M pieces ofthe segments among the frequency segments whose assignment evaluationvalues are large to the terminal apparatus.

The M segments assigned to each terminal apparatus is the segments inwhich the high communication quality is easy to be secured byscheduling, and many numbers of communication times are prospective, inall the N segments, and the M segments are a combination of the Msegments to increase the downlink throughput per each terminalapparatus. The reason why the indicator feedback is limited to the Msegments to each terminal apparatus is to reduce the enormous uplinkthroughput of the base station that is necessary for the indicatorfeedback, and to improve the uplink throughput of useful user data.

When the procedure to the frequency segment assignment is completed, thebase station apparatus transmits the data packets and the pilot signalsto be sent per each frequency segment decided by the scheduling of S7and the assignment result of the frequency segments determined in S9 asthe control signal to the terminal apparatus.

FIG. 13 shows an example of a message format to notify the assignmentresult of the frequency segments to the terminal apparatus. The firstMessage ID is the 8-bit value promised with the terminal apparatus, andthe purpose is to show that the following information is an ID of thefrequency segments assigned to the terminal apparatus. The second stageshows the terminal apparatus ID of the notification destination.AssignSegmentID #n (n being 0 to N−1, N being the number of all thesegments) after the third stage is a flag that shows 1 in the case ofthe frequency segment assigned to the terminal apparatus, and 0otherwise, and the terminal apparatus follows this notification, andfeeds back the instantaneous value of the downlink communicationquality.

The control explained above can be divided into two controls of theshort cycle and the long cycle.

The long cycle control to be accompanied with the statistics valuesfeedback of FIG. 8 is the control to limit the number of the segmentsfor feeding back the indicator of the communication capacityinstantaneous value per each terminal apparatus. FIG. 6 shows thecontrol sequence in which the part of the long cycle control isextracted from FIG. 5. The long cycle control includes the pilottransmission from the base station apparatus (S1), the communicationcapacity instantaneous value measurement by the terminal apparatus (S2),the statistics values update of the communication capacity (S3) and thestatistics values feedback to the base station apparatus (S5), theexpected value of the number of communication times calculation per eachsegment per each terminal apparatus (S8), the segment assignment fromthe fed back statistics values and the calculated expected value to theterminal apparatus (S9) and the notification of the assignment result(S10). The last pilot transmission (S12) has a function as a pilot fordetection of the slot and a function as the S1 in the next slot.

In addition, so as to start communications immediately, the terminalapparatus to which any frequency segment is not assigned can take theinstantaneous value of the communication capacity as the statistics andthe feedback is carried out by the message of FIG. 8, so that thefrequency segment assignment by the base station apparatus is carriedout. At this moment, the average value of the communication capacitybecomes the instantaneous value, and the standard deviation valuebecomes 0.

The short cycle control to be accompanied with the indicator feedback ofFIG. 9 is the control to decide the transmission destination terminalapparatus of the data packet per each downlink frequency segment, byscheduling per each slot. With regard to the indicator, the feedback iscarried out per each slot (or at a time interval at which thetransmission path change in the time direction is considered to be smallenough). However, the terminal apparatus to which any frequency segmentassignment is not carried out by the long cycle control (to which theassignment result is not notified) does not carry out the feedback.

The control at this short cycle is carried out according to the controlsequence shown in FIG. 7. FIG. 7 is a part of FIG. 5. The short cyclecontrol includes the pilot transmission from the base station apparatus(S1), the communication capacity instantaneous value measurement by theterminal apparatus (S2), the indicator creation of the instantaneousvalue (S4) and the feedback to the base station apparatus (S6), thescheduling based on the indicator (S7), and the data transmissionaccording to the scheduling result (S11). The last pilot transmission(S12) has a function as a pilot for detection of the slot and a functionas the S1 in the next slot.

FIG. 14 is one example of the embodiment of the terminal apparatusaccording to the present invention.

The received signal from the base station apparatus is converteddigitally by an analog-digital converter (ADC 101) after it goes throughthe analog signal process, a broadband signal is divided per eachfrequency segment by a downlink segment division part (Band Separator102), and the processes of the latter stage is carried out per eachfrequency segment. In the case of a downlink signal of OFDMA, thedownlink segment division part is realized by an FFT (Fast FourierTransform).

The received signal per each segment is separated into a pilot signaland other signal than the pilot by a downlink pilot separation part(DEMUX 103). The pilot signal is used for the calculation of theinstantaneous communication capacity of the frequency segment by aninstantaneous capacity calculation part (Capacity Measurement 106), andthe channel estimation by a downlink channel estimation part (ChannelEstimator 105). When a channel estimation result is inputted into adownlink demodulation decoding part (Demod & Decoder 104), the same partcarries out the detection of the signal, and through a demodulationdecoding process, the user data signal and the control signal arerecovered. The user data signal is stored into a memory (Memory 107),and the control signal transmitted from the base station apparatus isinputted into an indicator generation part (Indicator Generator 109) ofthe instantaneous communication capacity. The control signal inputtedinto the indicator generation part is a control signal transmitted inthe format of FIG. 13 from the base station apparatus, and it is a flagto show whether each segment is assigned to the terminal apparatus (itshows the segment to which the indicator should be fed back).

A statistics value calculation part (Calculator of statistics values108) of the communication capacity has a structure as shown in FIG. 15.The instantaneous value of the communication capacity is inputted fromthe instantaneous capacity calculation part (Capacity Measurement 106)of each frequency segment, and the accumulation of the instantaneousvalue and the accumulation of the square value of the instantaneousvalue are carried out. When an uplink control signal generation part(Control Channel Generator 110) reads the accumulation values, andcalculates the average value and the standard deviation value of thecommunication capacity per each frequency segment, a trigger to resetthe accumulation result is operated.

The indicator generation part (Indicator Generator 109) has a structureas shown in FIG. 16. First, the indicator generation part stores theinstantaneous value of the communication capacity from the instantaneouscapacity calculation part (Capacity Measurement 106) of each frequencysegment temporarily into a buffer. The indicator generation part refersto the assignment frequency segment information (FIG. 13) inputted fromthe downlink demodulation decoding part (Demod & Decoder 104), and skipsthe frequency segment that is not assigned to the terminal apparatus,and stores the value of the input buffer in the output buffer in theascending order of the segment numbers sequentially. The uplink controlsignal generation part (Control Channel Generator 110) refers to thevalue of the output buffer.

The uplink control signal generation part carries out the reference ofthe calculation result of the statistics value calculation part and theissue of the reset trigger at a long cycle, and carries out thereference of the output buffer of the indicator generation part at ashort cycle.

Herein, the explanation of FIG. 14 is made again.

The uplink control signal generation part (Control Channel Generator110) follows the formats shown in FIGS. 8 and 9 and creates a controlsignal, from the information that the statistics value calculation part(Calculator of statistics values 108) and the indicator generation part(Indicator Generator 109) generate, and carries out encoding andmodulation. The information of the indicator generation part istransmitted to the base station at one slot or a cycle following thesame. The information of the statistics value calculation part is readat a specified cycle, and reset to the statistics value calculationpart, and then, averaging to the read value and the standard deviationcalculation are carried out, and the control signal is sent to the basestation. Note that, since the above control signal is not a controlsignal peculiar to the frequency segment, it is treated as high priorityinformation, as a payload of the data signal of a certain segment. Sinceit is unclear whether the control information is sent at which uplinkfrequency segment, from perspective of the base station apparatus, it isnecessary to set the protocol with the base station apparatus (forexample, by promising by the message ID).

The uplink data signal generation part (Traffic Channel Generator 111)reads out the user data from the memory (Memory 107), and carries outencoding and modulation. The uplink pilot signal generation part (PilotChannel Generator 112) generates a known reference signal in the basestation apparatus.

The control signal, the data signal, and the pilot signal aremultiplexed by a time-multiplexing method and the like in an uplinkmultiplex signal generation part (MUX 113). The uplink segmentcombination part (Band Combiner 114) combines the signal after themultiplexing about all the uplink segments. In the case of an uplinksignal of OFDMA, the uplink segment combination part is realized by IFFT(Inverse Fast Fourier Transform). Note that, when the number of theuplink segments is 1, the uplink segment combination part becomesunnecessary. Thereafter, the signals pass a digital analog converter(DAC 115), and go through the analog signal process, and thentransmitted to the base station apparatus by a transmitting antenna.

Other parts than the analog digital converter, the digital analogconverter, and the memory among the terminal apparatuses can be realizedby DSP, FPGA or ASIC.

FIG. 17 is one example of an embodiment of the base station apparatusaccording to the present invention.

The received signal from the terminal apparatus is converted digitallyby an analog-digital converter (ADC 201) after it goes through theanalog signal process, a broadband signal is divided per each frequencysegment by an uplink segment division part (Band Separator 202), and theprocesses of the latter stage is carried out per each frequency segment.In the case of an uplink signal of OFDMA, the uplink segment divisionpart is realized by an FFT (Fast Fourier Transform). In addition, whenthe number of the uplink segments is 1, the uplink segment division partbecomes unnecessary.

The received signal per each segment is separated into a pilot signaland other signal than the pilot by an uplink pilot separation part(DEMUX 203). The pilot signal is used for the channel estimation by anuplink channel estimation part (Channel Estimator 204), and thedirection estimation per each terminal apparatus by an arrival directionestimation part (DOA Estimator 207). When a channel estimation result isinputted into an uplink demodulation decoding part (Demod & Decoder205), the same part carries out the detection of the received signal,and through a demodulation decoding process, the user data signal andthe control signal are recovered. The user data signal is stored into amemory (Memory 206), and with regard to the control signal, theindicator of the instantaneous communication capacity is inputted into ascheduler (Scheduler 211), and the statistics values of thecommunication capacity is inputted into a segment assignment part(Segment Assignment 210) respectively. The above operations, except forthe input to the segment assignment part of the communication capacitystatistic, are carried out at a short cycle in unit of slot.

The scheduler (Scheduler 211) chooses a terminal apparatus to become thecommunication partner per each frequency segment per each slot byalgorithm based on the Proportional Fairness. Before that, it isnecessary to convert the scheduler, based on the indicator of theinstantaneous communication capacity fed back by the terminal apparatus,into the transmission rate at which it is anticipated each terminalapparatus can communicate in each frequency segment. By a table in thesame manner as that in the prior art (refer to FIG. 18), the indicatoris converted into the anticipated transmission rate, except that theanticipated transmission rate of the frequency segment without thefeedback of the indicator is made 0.

An example of a concrete scheduling method is shown below.

When the downlink average transmission rate of a terminal apparatus u isdefined as aveR(u), and the anticipated transmission rate in a frequencysegment s is defined as instR(u, s), the evaluation function P(u, s) ofthe Proportional Fairness is expressed as follows.

$\begin{matrix}{{P\left( {u,s} \right)} = \frac{{\,_{inst}R}\left( {u,s} \right)}{{\,_{ave}R}(u)}} & {{Expression}\mspace{14mu} 4}\end{matrix}$

The u,s at which this value becomes maximum are chosen, and thefrequency segment s is assigned to the terminal apparatus u, and theaverage transmission rate aver (u) of the terminal apparatus u isupdated on assumption that the downlink transmission succeeds, and thenthe communication partners about the remaining frequency segments aredecided in the same manner.

By the above process, the terminal apparatus of the communicationpartner and the transmission rate are decided per each frequencysegment. At the same time, the number of the bits, the encoding rate,and the modulation method per each frequency segment are decidedaccording to FIG. 18. The user data to the terminal apparatus chosen pereach frequency segment is read out from the memory (Memory 206) for onlythe number of the bits equivalent to the transmission rate, and sent toa downlink data signal generation part (Traffic Channel Generator 213)of the corresponding frequency segment. At the same time, theinformation of the encoding rate and the modulation method is also sent.

Further, the ID of the terminal apparatus that the scheduler chooses pereach frequency segment is notified to a downlink control signalgeneration part (Control Channel Generator 212). By burying the terminalapparatus ID in the downlink control signal, the terminal apparatusmonitors the control signal, and it is possible to judge whether thedata to its own terminal apparatus are stored in the frequency segment.Thereby, since each terminal apparatus does not have to carry out thedemodulation decoding process of the frequency segments to which its owndata are not transmitted, effects such as the reduction of theelectricity consumption and the hardware scale of the terminal apparatusare expected.

The arrival direction estimation part (DOA Estimator 207) receives theuplink pilot signal from the terminal apparatus by an array antenna, andcarries out arrival direction estimation based on MUSIC (MUltiple SIgnalClassification) method. The pilot of any uplink frequency segment may beused, but the estimation precision becomes higher by choosing thefrequency segment whose receiving SINR is higher. The directionestimation result per each terminal apparatus is notified to the spatialdistribution analysis part (Spatial Distribution Analyzer 208). It isdesirable that the operation of the arrival direction estimation part isin a short cycle. When a frequency segment assignment is carried out toa certain terminal apparatus, if the direction of other terminalapparatuses is maintained at its latest state by short cycle update, itis possible to carry out the calculation of the expected value of thenumber of communication times more precisely, and precisely specify thefrequency segment that can secure more numbers of communication times,which leads to the improvement of the downlink throughput of theterminal apparatus.

An assignment information record part (Assign Record 209) is a memory torecord which terminal apparatus is assigned to each frequency segment.It is recorded by a segment assignment part (Segment Assignment 210),and it is referred to by the spatial distribution analysis part.

FIG. 19 is one example of the information that the spatial distributionanalysis part manages. It merges the direction estimation result pereach terminal apparatus and the assignment result of the frequencysegment. It records the number of terminal apparatuses assigned to eachfrequency segment, and the direction per each terminal apparatus.Separately from this, it also has the information of the arrivaldirection about the terminal apparatus of unassigned segment.

The spatial distribution analysis part (Spatial Distribution Analyzer208) calculates the expected value of the number of communication timeswhen it is supposed that the assignment of the frequency segment iscarried out to assume it a judgment material when frequency segments areassigned to all the terminal apparatuses. This calculation is carriedout at every time when a segment to feed back the indicator to theterminal apparatus is decided, in other words, at a long cycle.

FIG. 20 shows a case to assign a terminal apparatus (ID0) again from thestate of FIG. 19. The shaded hatch is the part changed from FIG. 19.When attention is paid to each frequency segment, the segment 0, towhich the terminal apparatus is already assigned, does not change, andas for the segments 1 and 2, the number of the terminal apparatusesincreases by 1. In all the frequency segments, when downlink packets aretransmitted by the Omni beam pattern, because all the other terminalapparatuses which are already assigned to each segment becomecompetitors, the expected value of the number of communication timesabout the terminal apparatus (ID0) is ½ with segment 0, ⅓ with segment1, and ¼ with segment 2. From the above, the expected value of thenumber of communication times about the terminal apparatus (ID0) issummarized as shown in FIG. 21A.

With FIG. 20 as assumption, now suppose the case in which the basestation apparatus carries out the spatial multiplex transmission by thedirectional beam. When the terminal apparatus whose angle difference is30 degrees or more with the terminal apparatus (ID0) is considered notto be a competitor, the expected value of the number of communicationtimes of segment 1 is ½ because the terminal apparatus (ID2) becomes itscompetitor, and the expected value of segment 2 is 1 because all theterminal apparatuses do not become competitors. Segment 0 is alsosimilar to segment 2. At this moment, the expected value of the numberof communication times about the terminal apparatus (ID0) is summarizedas shown in FIG. 21B.

The FIGS. 21A and 21B that are summarized as above are referred to bythe segment assignment part (Segment Assignment 210).

The segment assignment part (Segment Assignment 210) inputs thestatistic of the communication capacity from the uplink demodulationdecoding part (Demod & Decoder 205), and the expected value of thenumber of communication times from the spatial distribution analysispart (Spatial Distribution Analyzer 208), and carries out thecalculation shown in FIG. 12, and assigns M pieces of the frequencysegments per each terminal apparatus. The timing of the assignment iscarried out by the timing at which the statistics values of thecommunication capacity are inputted, and the old assignment is cancelledonce on this occasion. The assignment result is transmitted to adownlink control signal generation part (Control Channel Generator 212),and notified to the terminal apparatus as the message shown in FIG. 13.

The downlink control signal generation part (Control Channel Generator212) generates information including the terminal apparatus ID scheduledas the control signal peculiar to the frequency segment, from theinformation that the scheduler and the segment assignment part generate,and creates the control signal of the segment assignment resultaccording to the format shown in FIG. 13 as a control signal peculiar tothe terminal apparatus, and carries out encoding and modulation.

Because the control information (segment assignment information)peculiar to the terminal apparatus is not a control signal peculiar tothe segment, it is treated as high priority information, as a payload ofthe data signal of a certain segment. In order to handle suchinformation, the case when the frequency segment assignment is not donein the initial state is supposed too, and one frequency segment which iscommon to all the terminal apparatuses is prepared, and made the segmentthat is always assigned to all the terminal apparatuses. If there is notthe high priority control information, the user data signal may betransmitted.

The downlink data signal generation part (Traffic Channel Generator 213)carries out encoding and modulation on the bit groups sent from thescheduler, according to the encoding rate and the modulation method sentat the same time. The downlink pilot signal generation part (PilotChannel Generator 214) generates a known reference signal by theterminal apparatus.

The control signal, the data signal, and the pilot signal aremultiplexed by a time-multiplexing method and the like in a downlinkmultiplex signal generation part (MUX 215). The downlink segmentcombination part (Band Combiner 216) combines the signal after themultiplexing, about all the downlink segments.

In the case of a down signal of OFDMA, the downlink segment combinationpart is realized by IFFT (Inverse Fast Fourier Transform). Thereafter,the signals pass a digital analog converter (DAC 217), and go throughthe analog signal process, and then transmitted to the terminalapparatus from a transmitting antenna.

Further, in the case when the spatial multiplex communication is carriedout in the frequency segment, an array signal process is carried out tothe output of a downlink multiplex signal generation part (MUX 215). Adownlink segment combination part (Band Combiner 216), a digital analogconverter (DAC 217) and the analog signal process at the latter stagesare realized per each transmitting antenna element.

Other parts than the analog-digital converter, a digital analogconverter, and the memory, among the base station apparatuses may berealized by DSP, FPGA, and ASIC.

INDUSTRIAL APPLICABILITY

The present invention is realized in the base station apparatus and theterminal apparatus in the wireless communication system. In particular,it is effective in the broadband wireless communication system.

The invention claimed is:
 1. A method of wireless communication forcommunication between a base station and a plurality of terminalapparatuses, the method comprising: dividing an available frequency intoa plurality of segments and notifying control information to theterminal apparatus, the control information including setting of asegment of the plurality of segments, communication quality of whichwill be fed back by the terminal apparatus, and setting of a segment ofthe plurality of segments, communication quality of which will not befed back by the terminal apparatus; and feeding back communicationquality related to a predetermined segment to the base station inaccordance with the control information by the terminal apparatus. 2.The method of wireless communication according to claim 1, wherein thecontrol information includes information that indicates whethercommunication quality related to a segment is fed back or not and theinformation is provided to each segment.
 3. The method of wirelesscommunication according to claim 2, wherein the control informationincludes information of ‘1’ that indicates feeding back and ‘0’ thatindicates not feeding back, and either of the information is related toeach segment.
 4. The method of wireless communication according to claim1, wherein notifying control information to the terminal apparatus isperformed by using a frequency segment which has been previouslyallocated to a terminal.